R help - Jul 2010 - Function on columns of a dataframe

Hi,

I would like to assign the largest value of a column to a specific category
and repeat this for each column (v1 - v4).
> x=c(1:12)
>
cat=c("cat1","cat5","cat2","cat2","cat1","cat5","cat3","cat4","cat5","cat2","cat3","cat6")
> v1=rnorm(12,0.5,0.1)
> v2=rnorm(12,0.3,0.2)
> v3=rnorm(12,0.4,0.1)
> v4=rnorm(12,0.6,0.3)
> bla=data.frame(x,cat,v1,v2,v3,v4)
> bla
    x  cat        v1         v2        v3         v4
1   1 cat1 0.4013144 0.54839317 0.3946393  0.8679266
2   2 cat5 0.4595873 0.45788906 0.4030078  0.5919596
3   3 cat2 0.4542865 0.21516928 0.2777649  0.6112099
4   4 cat2 0.4787950 0.06252512 0.5095611  0.6450795
5   5 cat1 0.4910746 0.56591049 0.5151813  0.8465181
6   6 cat5 0.4194397 0.16592579 0.4361643  0.6415192
7   7 cat3 0.6148564 0.32240342 0.2690108  0.7114133
8   8 cat4 0.6174652 0.28076152 0.4577064 -0.2567284
9   9 cat5 0.4775395 0.28611768 0.4660210  0.4634120
10 10 cat2 0.4802962 0.03715569 0.4506361  1.0063235
11 11 cat3 0.6495094 0.33303172 0.3352933  1.4390324
12 12 cat6 0.4891481 0.45355589 0.3880739  0.7831656
> 
I can assign this by the sqldf() command for each column but I would like to
automate this as I have many columns.
> select=sqldf("select cat, max(v1) FROM bla GROUP BY cat")
> select
   cat   max(v1)
1 cat1 0.4910746
2 cat2 0.4802962
3 cat3 0.6495094
4 cat4 0.6174652
5 cat5 0.4775395
6 cat6 0.4891481
> 
Finally, I would like to have a dataframe where where the cat is followed by
each column maximum.

Thanks for your help!
-- 
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Hi Nils,
have a look at
?tapply
hth.

Am 09.07.2010 15:37, schrieb LogLord:
> Hi,
>
> I would like to assign the largest value of a column to a specific category
> and repeat this for each column (v1 - v4).
>
>   
>> x=c(1:12)
>>
cat=c("cat1","cat5","cat2","cat2","cat1","cat5","cat3","cat4","cat5","cat2","cat3","cat6")
>> v1=rnorm(12,0.5,0.1)
>> v2=rnorm(12,0.3,0.2)
>> v3=rnorm(12,0.4,0.1)
>> v4=rnorm(12,0.6,0.3)
>> bla=data.frame(x,cat,v1,v2,v3,v4)
>> bla
>>     
>     x  cat        v1         v2        v3         v4
> 1   1 cat1 0.4013144 0.54839317 0.3946393  0.8679266
> 2   2 cat5 0.4595873 0.45788906 0.4030078  0.5919596
> 3   3 cat2 0.4542865 0.21516928 0.2777649  0.6112099
> 4   4 cat2 0.4787950 0.06252512 0.5095611  0.6450795
> 5   5 cat1 0.4910746 0.56591049 0.5151813  0.8465181
> 6   6 cat5 0.4194397 0.16592579 0.4361643  0.6415192
> 7   7 cat3 0.6148564 0.32240342 0.2690108  0.7114133
> 8   8 cat4 0.6174652 0.28076152 0.4577064 -0.2567284
> 9   9 cat5 0.4775395 0.28611768 0.4660210  0.4634120
> 10 10 cat2 0.4802962 0.03715569 0.4506361  1.0063235
> 11 11 cat3 0.6495094 0.33303172 0.3352933  1.4390324
> 12 12 cat6 0.4891481 0.45355589 0.3880739  0.7831656
>   
>>     
> I can assign this by the sqldf() command for each column but I would like
to
> automate this as I have many columns.
>
>   
>> select=sqldf("select cat, max(v1) FROM bla GROUP BY cat")
>> select
>>     
>    cat   max(v1)
> 1 cat1 0.4910746
> 2 cat2 0.4802962
> 3 cat3 0.6495094
> 4 cat4 0.6174652
> 5 cat5 0.4775395
> 6 cat6 0.4891481
>   
>>     
> Finally, I would like to have a dataframe where where the cat is followed
by
> each column maximum.
>
> Thanks for your help!
>   
-- 
Eik Vettorazzi
Institut f?r Medizinische Biometrie und Epidemiologie
Universit?tsklinikum Hamburg-Eppendorf

Martinistr. 52
20246 Hamburg

T ++49/40/7410-58243
F ++49/40/7410-57790